Note: Descriptions are shown in the official language in which they were submitted.
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PATENT APPLICATION
Attorney Docket No. D/90210
SHORT PAPER PATH ELECTRONIC DESKEW SYSTEM
This invention relates generally to a sheet deskewing system,
and more particularly concerns a short paper path electronic deskewing
system for use in an electrophotographic printing machine.
In a typical electrophotographic printing process a
photoconductive member is charged to a substantially uniform potential so
as to sensitize the surface thereof. The charged portion of the
photoconductive member is exposed to a light image of an original
document being reproduced. Exposure of the charged photoconductive
member selectively dissipates the charges thereon in the irradiated areas.
This records an electrostatic latent image on the photoconductive member
corresponding to the informational areas contained within the original
document. After the electrostatic latent image is recorded on the
photoconductive member, the latent image is developed by bringing a
developer material into contact therewith. Generally, the developer
material comprises toner particles adhering triboelectrically to carrier
granules. The toner particles are attracted from the carrier granules to the
latent image forming a toner powder image on the photoconductive
member. The toner powder imac~e is then transferred from the
photoconductive member to a copy sheet. The toner particles are heated
to permanently affix the powder image to the copy sheet.
In a commercial printing machine of the foregoing type, paper
handling devices of the type including xerographic reproduction machines
have incorporated some sort of registration system to properiy align sheets
of paper passing through these devices. Whether the sheet is a document
in a recirculating document handler or a copy sheet in the reproduction
processor, registration or alignment of the sheets traveling through a paper
path to a known orientation is necessary for the achievement of high
quality copying. Wlth particular reference to the reproduction processor, t
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will be appreciated that registration of copy sheets must include, for
example, synchronization of the copy sheet edges with the latent image on
the photoreceptor, as well as speed matching with the photoreceptor and
transportation of the sheet into the transfer zone or deskewing of
improperly fed copy sheets.
In a typical registration transport, a force is applied on the copy
sheets to move them to a fixed registration edge as the sheets are
simultaneously moved through the machine. In the past, alignment
systems have been primarily passive, making use of physical contact with
the sheet for alignment generally by providing a fixed position contacting
registration member at an appropriate position for a selected registration
operation. Such contacting members have included gripper bars, side
guides, tamper arrangements, stalled rolls and/or registration fingers. A
common weakness in all these devices is the inherent relative motion
between the registration member and the sheet during contact. Contact
and slippage between registration member and sheet can cause
unacceptable damage to the sheet edge, and potential jamming of the
machine. In certain finger registration systems, misfeeding may lead to
tearing, ripping or holing of the sheet, particularly problematic when
handling originals. Additionally, long term contact between passing sheets
and the registration member may cause wear of the registration member,
leading to long term variance in registration, thereby requiring adjustment
or repair of the mechanical members to obtain original registration
accuracy. Many of these arrangements often also require extended paper
paths to be effective.
The following disclosures may be relevant to various aspects of
the present invention:
US-A-4,971 ,304
Patentee: Lofthus
Issued: November 20, 1990
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US-A-4,438,-917
Patentee: Janssen, et al.
Issued: March 27,1984
US-A-4,216,482
Patentee: Mason
Issued: August S,1980
J P-63-82255
Patentee: H i royosh i Maruyama
Issued: April 13,1988
JP-57-175643
Patentee: Eisaku Saiki
Issued: October 28,1982
~ he relevant portions of the foregoing disclosures may be briefly
summarized as follows:
US-A-4,971,304 discloses a method and apparatus for deskewing
and side registration in which a sheet with a random skew is driven
nondifferentially until skew is measured. The sheet is then driven
differentially by independent rollers to a known skew and to a side
registration point, at which time the sheet is driven differentially to
compensate for the known skew.
US-A-4,438,917 discloses a sheet deskewing arrangement
provided with a sensor set arranged along the path of sheets in the
processing direction and a pair of selectable controllable motors, each
driving a driving nip in a roll pair, supported to contact a side portion of thesheet in driving engagement, to correct skew sensed by the sensors. The
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two sensors, arranged in a line perpendicu~ar to the path of sheet travel,
each detect when the lead edge of a sheet passes thereby. A difference in
sensing time of sheet passage by each sensor is indicative of sheet skew,
and the two motors are driven in accordance with the difference to
accelerate or decelerate a side portion of the sheet, thereby rotating the
sheet to bring the lead edge of the sheet i nto registration.
US-A-4,216,482 teaches a combination of a hard stopping pivot
member and a positive driving arrangement, coupled with fixed and
movable sensors to register a sheet.
JP-63-82255 discloses the use of independently driven timing
rollers which are rotatable in either a clockwise or counterclockwise
direction to align a sheet.
JP-57-175643 describes a stalled roll technique of deskewing
whereby the leading edge of a sheet is fed into the bite point of a set of
stationary rollers causing the sheet to be deformed and to align by means
of force supplied by a paper buckle along the stationary rolls at which time
the rolls are activated and the sheet driven to the next station or set of rolls.
The independently driven rolls of the above references require
either a long paper path or elaborate nip releases in order to function
properly. The stalled roll devices utilize a paper buckle to supply a
registration force to the lead edge of a sheet to achieve proper alignment.
Additionally, in the case of the stalled roll or fixed pivot point devices, sheet
damage is likely to occur, especially when lighter weight sheets are
handled.
In accordance with one aspect of the present invention, there is
provided an apparatus for deskewing and side registering a sheet. The
apparatus comprises means for advancing the sheet along a primary sheet
feeding path. Means, operatively associated with the advancing means
measures the deviation of the sheet from the primary sheet feeding path
when at least a portion of the sheet is positioned within the advancing
means. Means, responsive to the measuring means, control the advancing
means to restore the sheet to the primary sheet feeding path.
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Pursuant to another aspect of the present invention, there is
provided an electrophotographic printing machine of the type in which a
sheet is deskewed and side registered. The improvement comprises means
for advancing the sheet along a primary sheet feeding path. Means,
operatively associated with the advancing means measures the deviation of
the sheet from the primary sheet feeding path when at least a portion of
the sheet is positioned within the advancing means. Means, responsive to
the measuring means, control the advancing means to restore the sheet to
the primary sheet feeding path.
Other features of the present invention will become apparent as
the foilowing description proceeds and upon reference to the drawings, in
which:
Figure 1 is a schematic elevational view depicting an illustrative
electrophotographic printing machine incorporating the sheet deskewing
apparatus of the present invention therein; and
Figure 2 is a top view of the present invention showing the
relationship between the sheet sensors, standard drive rolls and
independently driven drive rolls of the present invention; and
Figure 3 is a side elevation of Figure 2 along line A-A showing
the t~uckle in the sheet between the roll sets.
While the present invention will be described in connection with
a preferred embodiment thereof, it will be understood that it is not
intended to limit the invention to that embodiment. On the contrary, it is
intended to cover all alternatives, modifications, and equivalents as may be
included within the spirit and scope of the invention as defined by the
appended claims.
For a general understanding of an electrophotographic printing
machine in which the features of the present invention may be
incorporated, reference is made to Figure 1 which depicts schematically the
various components thereof. Hereinafter, like reference numerals will be
employed throughout to designate identical elements. Although the
apparatus for selecting copy sheets is particularly well adapted for use in
the electrophotographic printing machine of Figure 1, it should become
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evident from the following discussion that it is equally well suited for use in
a wide variety of devices and is not necessarily limited in this application to
the particular embodiment shown herein.
Since the practice of electrophotographic printing is well known
in the art, the various processing stations for producing a copy of an
original document are represented in Figure 1 schematically. Each
processing station will be briefly described hereinafter.
As in all electrophotographic printing machines of the type
illustrated, a drum 10 having a photoconductive surface 12 entrained about
and secured to the exterior circumferential surface of a conductive
substrate is rotated in the direction of arrow 14 through the various
processing stations. By way of example, photoconductive surface 12 may
be made from selenium. A suitable conductive substrate is made from
aluminum.
Initially, drum 10 rotates a portion of photoconductive surface
12 through charging station A. Charging station A employs a conventional
corona generating device, indicated clenerally by the reference numeral 16,
to charge photoconductive surface 12 to a relatively high substantially
uniform potential.
Thereafter drum 10 rotates the charged portion of
photoconductive surface 12 to expose station B. Exposure station B
includes an exposure mechanism, indicated generally by the reference
numeral 18, having a stationary, transparent platen, such as a glass plate or
the like for supporting an original document thereon. Lamps illuminate
the original document. Scanning of the original document is achieved by
oscillating a mirror in a timed relationship with the movement of drum 10
or by translating the lamps and lens across the original document so as to
create incremental light images which are projected through an apertured
slit onto the charged portion of photoconductive surface 12. Irradiation of
the charged portion of photoconductive surface 12 records an electrostatic
latent image corresponding to the informational areas contained within
the original document. Obviously, electronic imaging of page image
information could be used, if desired.
~ v ~ ~ l ~ . " ~ ~ ~ c vv ~ v ~ , " ~
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Drum 10 rotates the electrostatic latent image recorded on
photoconductive surface 12 to development station C. Development
station C includes a developer unit, indicated generally by the reference
numeral 20, having a housing with a supply of developer mix contained
therein. The developer mix comprises carrier granules with toner particles
adhering triboelectrically thereto. Preferably, the carrier granules are
formed from a magnetic material with the toner particles being made from
a heat settable plastic. Developer unit 20 is preferably a magnetic brush
development system. A system of this type moves the developer mix
through a directional flux field to form a brush thereof. The electrostatic
latent image recorded on photoconductive surface 12 is developed by
bringing the brush of developer mix into contact therewith. In this manner,
the toner particles are attracted electrostatically from the carrier granules
to the latent image forming a toner powder image on photoconductive
surface 12.
With continued reference to Figure 1, a copy sheet is advanced
by sheet feeding apparatus 60 through the paper path which includes drive
rolls 34 and 36 to registration roller 24 and idler roller 26. Registration
roller 24 is driven by a motor (not shown) in the direction of arrow 28 and
idler roller 26 rotates in the direction of arrow 38 since roller 26 is in contact
therewith. In operation, feed device 60 operates to advance the copy sheet
from the selected tray through the guide and path along which rolls 34 and
36 are located and then into registration roller pairs 24, 26 and 25, 27 such
that the sheet is forwarded toward the drum 12 in synchronism with the
image of the drum. The sheet is advanced in the direction of arrow 43
through a chute formed by guides 29 and 40 to transfer station D.
Continuing now with the various processing stations, transfer
station D includes a corona generating device 42 which applies a spray of
ions to the back side of the copy sheet. This attracts the toner powder
image from photoconductive surface 12 to copy sheet.
After transfer of the toner powder image to the copy sheet, the
sheet is advanced by endless belt conveyor 44, in the direction of arrow 43,
to fusing station E.
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Fusing station E includes a fuser assembly indicated generally by
the reference numeral 46. Fuser assembly 46 includes a fuser roll 48 and a
backup roll 49 defining a nip therebetween through which the copy sheet
passes. After the fusing process is completed, the copy sheet is advanced by
rollers 52, which may be of the same type as registration rollers 24 and 26,
to catch tray 54.
Invariably, after the copy sheet is separated from
photoconductive surface 12, some residual toner particles remain adhering
thereto. These toner particles are removed from photoconductive surface
12 at cleaning station F. Cleaning station F includes a corona generating
device (not shown) adapted to neutralize the remaining electrostatic
charge on photoconductive surface 12 and that of the residual toner
particles. The neutralized toner particles are then cleaned from
photoconductive surface 12 by a rotatably mounted fibrous brush (not
shown) in contact therewith. Subsequent to cleaning, a discharge lamp
(not shown) floods photoconductive surface 12 with light to dissipate any
residual electrostatic charge remaining thereon prior to the charging
thereof for the next successive imaging cycle.
It is believed that the foregoing description is sufficient for
purposes of the present application to illustrate the general operation of
an electrophotographic printing machine. Referring now to the specific
subject matter of the present invention, Figure 2 depicts the deskewing
system in greater detail.
Turning now to Fig. 2, the relationship of the commonly driven
roll pairs 34, 36 and 35, 37, the independently driven roll pairs 24, 26 and
25,27, and the sheet sensors 96 and 97 can be seen . A sheet 100 is shown i n
the control of both sets of drive rolls and is traveling in the direction noted
by arrow 43.
The deskew roll pairs 24, 26 and 25, 27 are driven at a speed
equal to the drive roll pairs 34,36 and 35,37 in the direction 43 as the sheet
enters the nips of the deskew roll pairs 24, 26 and 25, 27. After the sheet
100 enters the deskew roll nips, the deskew roll pairs 24,26 and 2S,27 slow,
creating a paper buckle 102 between the deskew roll pairs and the
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preceding set of drive rolls 34, 36 and 35, 3Z. Sensors 96 and 97 determine
skew angle of the sheet and direct the motor controllers 84,85 to adjust the
speed of the independent drive motors 86, 87.of the deskew roll pairs 24,
26 and 25,27 so as to bring the sheet 100 into proper aiignment. As a result
of the buffer zone created by the paper buckle 102, it is not necessary that
the trailing edge 101 of the sheet 100 have passed through the prior set of
drive rolls 34, 36 and 35, 37, nor is it necessary that any elaborate or
complicated nip release mechanisms be utilized to allow the sheet to be
deskewed without damage to the sheet. The sheet buckle isolates the
motion occurring in the deskew nips.
The paper buckle buffer zone is illustrated in Fig. 3, which is a
side view of Fig. 2 taken along line A-A. It is important to note that in the
present invention the buckle 102 illustrated in Fig. 3 is not used to provide
an alignment force as in the stalled rolled techniques of prior inventions.
Rather, the buckle 102 acts solely as a buffer zone to prevent damage to the
sheet 100 while the deskew roll pairs 24, 26 and 25, 27 are correcting the
alignment of the sheet 100. Since the deskew rolls 24,26 and 25,27 initially
are rotating at the same speed as the preceding drive rolls 34,36 and 35,37,
there is no damage to the lead edge of the sheet as it enters the nips of the
deskew rolls 24,26 and 25,27, even for very lightweight sheets.
It is furthermore possible to also provide for a side registration
alignment through the use of the sensors of the present invention so as to
cause the sheet to be aligned at a precise lateral position as it is passing
through the deskew rolls. The advantage of the this method is the
elimination of the necessity for a registration edge, which edges are usually
stationery and have the potential for sheet damage as a result of the
relative movement between the edges and the sheet.
In recapitulation, there is provided a method for short paper
path deskewing, which involves utilizing a set of independently driven
deskew rolls. The deskew rolls are initially driven at a speed equal to the
prior sheet transport rolls until the sheet enters the nips of the deskew rolls.After the sheet enters the deskew rolls, the deskew rolls slow, causing a
paper buckle or buffer zone to be formed between the deskew rolls and
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the prior drive rolls. Sensors mounted immediately after the deskew rolls
determine the skew angle of the sheet and signal the independently driven
deskew roll motor controllers to adjust speed so as to bring the sheet into
proper alignment. Due to the buffer zone created by the buckle between
the deskew rolls and the prior set of drive rolls, it is not necessary that the
trailing edge of the sheet have passed beyond the prior drive rolls nor are
any complicated nip release mechanisms necessary. It is further possible to
utilize the deskew rolls and sensors to insure proper lateral alignment or
side registration of the sheet without the necessity of a fixed registration
guide which has the potential for damage to the sheet.
It is, therefore, apparent that there has been provided in
accordance with the present invention, an apparatus and method that fully
satisfies the aims and advantages hereinbefore set forth. While this
invention has been described in conjunction with a specific embodiment
thereof, it is evident that many alternatives, modifications, and variations
will be apparent to those skilled in the art. Accordingly, it is intended to
embrace all such alternatives, modifications and variations that fall within
the spirit and broad scope of the appended claims.
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